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Error code reference

Denso Air Conditioner Error Code E4

Activation of protective device

Denso codesDenso air conditioner codes

Activation of protective device — fan motor current is abnormal (higher than overcurrent relay's current setting value).

First step from the service manual

See troubleshooting chart on page 47. To reset: hold down SET TEMP UP and DOWN buttons simultaneously for 3 seconds.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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What E4 means on a Denso air conditioner

The E4 error code on a Denso air conditioner signals that the protective device for the fan motor circuit has activated due to an abnormal current draw. Specifically, the current flowing through the fan motor has exceeded the threshold set by the overcurrent relay. This relay is a safety component designed to interrupt operation before excessive current causes motor winding damage, insulation failure, or a fire hazard. When E4 triggers, the unit will shut down and hold this fault state until the condition is addressed and the code is manually cleared.

The fan motor is responsible for moving air across the evaporator or condenser coil, depending on which fan circuit is affected. When the motor draws more current than the relay's preset limit, it typically points to mechanical resistance in the fan assembly, an electrical fault within the motor windings, or a problem with the capacitor that assists motor startup. A motor that is beginning to fail will often show elevated current draw before it fails completely, making E4 an early warning that should not be ignored.

Diagnosing E4 requires following the troubleshooting chart on page 47 of the Denso service documentation. Technicians should measure running current against the relay's rated setpoint, inspect fan blades for obstruction or damage, check motor winding resistance for shorts or opens, and test the run capacitor if equipped. To reset the fault after repairs, press and hold the SET TEMP UP and DOWN buttons simultaneously for 3 seconds.

Source: manufacturer service documentation.

Common causes of E4

  1. 01

    Worn or failing fan motor

    Part replacement

    As fan motor bearings wear out, internal friction increases, causing the motor to draw higher current to maintain speed. Sluggish or noisy fan rotation is a common indicator.

  2. 02

    Fan blade obstruction or damage

    Wiring / connection

    Debris lodged against the fan blade or a bent blade contacting the housing creates mechanical resistance, forcing the motor to work harder and exceed the overcurrent relay threshold.

  3. 03

    Failed or degraded run capacitor

    Part replacement

    A weak or failed capacitor reduces the starting torque and running efficiency of the fan motor, causing it to pull abnormally high current. Capacitor failure can often be confirmed with a capacitance meter.

  4. 04

    Shorted motor windings

    Part replacement

    A partial short in the motor windings lowers winding resistance and allows excessive current to flow. This can be checked by measuring winding resistance with a multimeter.

  5. 05

    Overcurrent relay set too low or faulty

    Part replacement

    If the overcurrent relay has drifted from its correct setpoint or has become defective, it may trip at normal operating currents. Verify the relay's current setting against the motor's rated operating current before replacing other components.

See the test procedure for each cause

Frequently asked questions about E4

What does E4 mean on a Denso air conditioner?
E4 indicates that the fan motor's current draw has exceeded the threshold of the overcurrent relay, causing the protective device to activate and shut the unit down. This is a safety response to prevent motor or electrical damage from sustained high current. The unit will remain off until the fault is diagnosed and the code is manually reset.
Can I fix the E4 error myself, or do I need a technician?
Some causes, such as a blocked or obstructed fan blade, can be safely inspected and cleared by a knowledgeable homeowner. However, diagnosing electrical faults like shorted motor windings, a failed capacitor, or a miswired overcurrent relay requires electrical testing equipment and familiarity with AC circuits. If you are not comfortable working with electrical components, it is best to contact a qualified HVAC technician.
Is it safe to keep using my Denso air conditioner when E4 appears?
No. The E4 code indicates the unit has already shut itself down as a protective measure. Attempting to bypass or repeatedly reset the fault without addressing the root cause risks motor burnout, damage to other electrical components, and in serious cases, a fire hazard. The system should remain off until the cause of the abnormal current draw is identified and corrected.
Will resetting the E4 error code fix the problem?
Resetting the code by holding the SET TEMP UP and DOWN buttons simultaneously for 3 seconds will clear the fault and allow the unit to restart, but it does not fix the underlying issue. If the root cause of the high current draw is still present, the overcurrent relay will trip again and E4 will return. The reset should only be performed after the problem has been diagnosed and repaired.
How much does it cost to repair a Denso air conditioner with an E4 error?
Repair costs depend on which component is at fault. A run capacitor replacement is typically the least expensive fix, often ranging from $75 to $200 including labor. Fan motor replacement is more involved and can range from $200 to $600 or more depending on the motor cost and labor rates in your area. Having a technician perform a current draw test and inspect the fan assembly first can help narrow down costs before committing to parts.

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